1. Field of Invention
The invention is directed to an apparatus and method for attribute identification. More specifically, the invention is directed to an apparatus and method which identifies at least one attribute of an article so that the article may be accurately reproduced.
2. Description of Related Art
Color detection in reproduction devices, such as color scanners and photocopiers, is generally known in the art. As illustrated in FIG. 1, a conventional color scanner includes a light source 100 which illuminates an image on a medium 110. The light beam 102 that is incident upon the image is reflected and imaged by an optical system 104 down upon a CCD sensor 120. These conventional scanners use many different methods and apparatus to detect the colors of the image.
For color scanners to properly convert the color image to electronic signals, the color scanners need to simulate the color response of the human eye. This is conventionally done by scanning the color image with the three separate color channels, usually red, green and blue channels.
As shown in FIG. 2, the CCD sensor 120 of the conventional color scanner has three rows 122, 124 and 126 of detectors over which three different color filters, a red filter R, a green filter G, and a blue filter B, are placed. Thus, the color scanner has separate areas of the sensor for sensing particular color components of the image being scanned.
Another approach taken by the prior art is shown in FIG. 3. In this device, the CCD sensor 120 does not have any color filters on the rows 122, 124 and 126 of the detectors. Instead, a color wheel 130 is placed in the optical path of the light beam 102 between the light source 100 and the CCD sensor 120. The color wheel 130 contains three filters, a red filter 132, green filter 134 and blue filter 136. The color wheel 130 is rotated through the optical path to provide the proper color separation. This device requires three scans of the image in order to obtain information on all three colors.
In another approach, as shown in FIG. 4, a conventional color scanner uses three filters, a red filter 142, green filter 144 and blue filter 146. These filters are moved into and out of the optical path of the light beam 102 between the light source 100 and the CCD sensor 120. By sliding the filters 142, 144 and 146 into and out of the optical path, information for each color of the image can be obtain in three scans of the image.
However, since the color filters of conventional scanners do not exactly match the spectral response of the human eye, only an imperfect conversion from the scanner output to a colormetric response (human eye) can be obtained. For accurate color representation, it is necessary to have a color scanner with a color response that matches the human eye. If a color scanner can accurately match the color response of the human eye, the color scanner can create an electronic file that completely describes the color of an object as seen by the human eye. Thus, the image can be reproduced accurately by a printer, a photocopier, or a display.
Recently, an approach has been suggested in U.S. Pat. No. 5,642,197 to Tuhro et al., which is shown in FIG. 5. Tuhro suggests using a filter 150 in addition to the red, green and blue filters 132-136 of the color wheel 130 to obtain corrected color values. Specifically, Tuhro's approach requires an initial scan of the image using a set of red, green and blue filters, and then subsequent scans using the red, green and blue filters with the additional filter 150 placed in the optical path. The additional filter 150 provides offset color values that may be used to calculate corrected color values. In another embodiment of Tuhro, shown in FIG. 6, the color wheel 130 is equipped with an additional red filter 133, an additional green filter 135 and an additional blue filter 137 to provide the offset values. This approach requires many additional scans of the image, for example up to six scans of the image, thus slowing down the reproduction process.